This invention relates generally to a cryogenic fluid container, and more particularly concerns a cryogenic fluid container having means for relieving the internal head pressure during filling in order to fill completely the cryogenic container with cryogenic liquid.
Gases, having low boiling points at atmospheric pressure, such as carbon dioxide (CO.sub.2) and oxygen (O.sub.2), for example, present many difficulties and problems not encountered in handling ordinary gases. In order to provide CO.sub.2 gas for use in fast food restaurants for carbonating soft drinks, for example, it has been necessary in the past to provide the compressed CO.sub.2 in single or clustered high pressure containers which are really best suited for customers with low consumption or sporadic use. Such service is expensive because of the high cost of handling the necessary heavy containers the weight of which is very high in comparison to the weight of the compressed gas contained therein.
Customers having high or moderately high demands for O.sub.2 or CO.sub.2 gas have also been serviced by means of high pressure tubular receivers installed on their premises. Such receivers are periodically serviced by means of a pump equipped liquid tank truck which transports the material to the customer's premises in liquid form and charges such receivers with high pressure gas drawn from the vaporized liquid. These tank trucks must be specially equipped for this service and represent a large capital expense. Furthermore, the delivery of gas is time consuming owing to the limiting capacity of the portable high pressure pumps.
Another way of storing such low boiling point gases, such as O.sub.2 and CO.sub.2, is to store them in a cryogenic tank in liquid form on the user's premise. Such a cryogenic tank includes an inner vessel which holds the cryogenic liquid and an outer vessel within which the inner vessel is supported. There is an insulating space between the inner and outer vessels in which a vacuum is drawn and insulating material is positioned. Because of the low heat transfer from the ambient atmosphere outside of the outer vessel to the contents of the inner vessel, the liquid O.sub.2 or CO.sub.2 can remain in liquid form for some period of time before heat vaporization causes the vapor pressure of the O.sub.2 or CO.sub.2 to exceed a preset maximum pressure and to activate a regulator system for maintaining the vapor pressure within a safe range.
When such a cryogenic tank is installed on a customer's premises, such as a CO.sub.2 tank in a fast food restaurant, it is necessary periodically to refill the cryogenic tank with liquid CO.sub.2. The CO.sub.2 tank is filled by means of a delivery truck carrying CO.sub.2 liquid which makes its rounds from one customer to the next. In order to achieve the greatest efficiency, it is important to be able to fill the customer's tank as nearly full as possible without resorting to sophisticated high pressure pumps and/or regulator systems.
One way of filling of the cryogenic tank on the customer's premises is to attach, a single hose from the cryogenic tank on the transport truck to the inlet of the customer's cryogenic tank. The vapor pressure in the transport tank forces the liquid from the transport tank into the cryogenic tank on the customer's premises. As the liquid flows into the customer's cryogenic tank, the increasing volume of liquid in the customer's cryogenic tank compresses the vapor above the liquid into a smaller and smaller space until the vapor pressure in the customer's tank exactly equals the vapor pressure in the transport tank. At that point, transfer from the transport tank to the customer's tank ceases even though the customer's tank may be only partially full.
In order to relieve the vapor pressure in the customer's cryogenic tank, the prior art suggests various ways of liquifying the CO.sub.2 vapor in the top of the customer's tank by means of eductors, J-shaped bubbler tubes, or J-shaped sprinkler tubes, all of which are shown in Remes et al. Ser. No. 448,729, filed Dec. 10, 1982.
Other cryogenic fluid systems have required the necessity of a high pressure pump on the delivery truck to increase the delivery pressure along with a skilled operator to vent the customer's tank to assure that it is completely filled.